1. Field of the Invention
The present invention relates compositions and methods for producing water soluble fluorescent quantum carbon dots (C-dots). In particular, the present invention relates to the production of water soluble C-dots using a carbon nano tube production method followed by filtration and oxidation. The C-dots are self fluorescing and can be modified to produce a range of color fluorescences.
2. Description of Related Art
Quantum dots are the subject of much research and investigation using a wide variety of materials. Several different materials are being used in an attempt to convert them into a quantum confined type dot. Quantum sized carbon dots are roughly defined as nano sized carbon dots with a diameter in the range of 2 to 10 nanometers and comprised of spherical form of very small size but larger than fullerene made out of graphene sheets of very small size. Previously C-dots have been produced by laser beam ablation of a carbon target. The carbon target is prepared by hot-pressing a mixture of graphite powder and cement, followed by a stepwise baking, curing and then annealing in an argon flow A laser. The laser is used for the ablation during which the carbon target is in a flow of argon gas carrying water vapor (usually through a water bubbler) at 900° C. and 75 kPa. However, this technique chiefly produces nano scale carbon particles to be treated further to produce a C-dot suspension and further surface passivation by attaching organic molecules. None of these types of C-dots are capable of self fluorescing.
These known materials are produced with techniques that are not only difficult to consistently repeat but do not lend themselves to practical mass producing. In addition starting material synthesis is difficult and the entire process is expensive because of the materials and temperatures needed. To date a practical production of C-dots has not been discovered.
Currently, C-dots are not self fluorescent but are caused to fluoresce by addition of a coating, by surface modification or by addition of a fluorescent molecule, such as a bacterial produced green fluorescent protein. This approach adds extra costs as well as complexity and is limited in the color change achievable with each technique.
It was reported (Ya-Ping Sun et al, J. American Chemical Society, 2006, 128, 7756-7757) that quantum-sized carbon dots are soluble in water and show bright and colorful photoluminescence only because of passivation of these carbon nano particles by organic molecules. Therefore, conventionally prepared carbon dots are not applicable to practical use as self fluorescent material.
Carbon nanotubes have been isolated from carbon soot by solvent washing. That production is described in U.S. patent application Ser. No. 11/680,888 filed Mar. 1, 2007 and incorporated herein by reference in its entirety. There is no reference to the existence or isolation of quantum materials of any kind.